I think that a project is corrupt when is only that project the one that cause problems. When I got problems with not only one project, them I think about the system and the application. And if what is corrupted is the project, trash the prefs is for nothing. And when I think that the project is corrupted, I open a new project and I drag everything from the brownser of the crrupted project to the new one. Save it and open it. Its works the 95% (?) of the times. Why? I don’t kno, but its works.
I belive than at least the 75% of the problems with FC happens because the system is not optimized. Boots in safe mode, repairing permisions, running maintenace and Diskwarrior o Techtools are things to do before to think about re-installing FC. And I think that trash the preffs is the last thing.
If you want to trash the prefss, you must go to Users>Your account>Librari>Prefferences>Final Cut Pro User Data>
There you got three docs with the FCs thunbnail (Final Cut Pro 5.0 Prefs/Final Cut Pro Obj Cache/Final Cut Pro Prof Cache). Those are the docs that you must trash.
I think that your RAM can be giving you problems. 4.5Gbs RAM can not be paired as is recommended.
Cheers,
rafael